Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.92	7.329%	$260.7236	$260.72	$260.70	$260.70
Purchase #2	$47.68	9.270%	$52.0999	$52.10	$52.10	$52.10
Purchase #3	$148.59	11.397%	$165.5248	$165.52	$165.50	$165.50
Purchase #4	$88.85	4.706%	$93.0313	$93.03	$93.05	$93.00
Purchase #5	$89.48	10.111%	$98.5273	$98.53	$98.55	$98.50
Purchase #6	$222.56	7.263%	$238.7245	$238.72	$238.70	$238.70
Purchase #7	$163.57	10.212%	$180.2738	$180.27	$180.25	$180.30
7 purchase totals =	$1,003.65		$1,088.9052	$1,088.89	$1,088.85	$1,088.80